The present invention relates to an injurious insect-control method for controlling the proliferation of the injurious insect by disturbing the communication of the injurious insect for copulation through release of the sex pheromone of the insect from a source thereof distributed over a field.
The copulation of an injurious insect can be disturbed by releasing, in a large amount, the sex pheromone of the insect which is emitted by the female insect for making the male insect realize the location of the former. Such an injurious insect-control method has recently become of major interest since it allows the reduction of the amount of an agricultural chemical used in a field for controlling an injurious insect and has been considered to be a promising method.
Conventionally, there has seldom been investigated any method for effectively controlling an injurious insect by rationally distributing a sex pheromone-release agent throughout a very wide field. It is not easy to distribute, for instance, an agent for releasing the sex pheromone of a specific injurious insect over a field. In addition, the labor and time required for the distribution thereof in a field increase in proportion to the area of the field which requires the control of the injurious insect.
There have been developed so-called spray type sex pheromone-release agents which are subjected to the aerial application for the purpose of saving the labor required for the distribution of the agents over fields. However, this aerial distribution of the spray type sex pheromone-releasing agent does not ensure a sufficient injurious insect-control effect. The effects of the spray type sex pheromones are greatly influenced by various external factors such as meteorological conditions. For this reason, it is very difficult to appropriately select the time for distributing the sex pheromone-releasing agent and any desired effect thereof would not be anticipated when missing the chance for its application. There has been known an agent having a long effective period. In this case, however, the agent suffers from a variety of problems. For instance, the amount of the agent released per unit time period lacks in uniformity.
The object of the present invention is to eliminate the foregoing drawbacks associated with the conventional methods and more specifically to provide a method for rationally controlling injurious insects which permits the reduction of the labor and time required for the distribution of the sources of sex pheromones of these injurious insects over fields to be controlled and which permits effective control of the injurious insects.
The method for controlling an injurious insect according to the present invention comprises disturbing the copulative communication of the insect to prevent proliferation of the insect by distributing a source of the sex pheromone thereof over a field to thus make the sex pheromone release from the source distributed in the field, wherein a source of the sex pheromone having a high effective component-release rate per unit time is distributed over the central region of the field at a low density while a source of the sex pheromone having a low effective component-release rate per unit time is distributed over the peripheral region of the field at a high density.
In a preferred embodiment according to the present invention, a sex pheromone-release agent having an effective component-release rate ranging from 0.01; to 2 g/day may be distributed over the central region of a field at a density ranging from 1 to 50 locations/ha, while a sex pheromone-release rope having an effective component-release rate ranging from 5 to 250 mg/m/day may be stretched around the peripheral region of the field at a density ranging from 10 to 150 m/ha.
The injurious insect-control method according to the present invention comprises the step of distributing the sources of the sex pheromone of an injurious insect over a field. The kinds of effective components of the sex pheromone-release agents to be distributed in a field are appropriately selected depending on the kinds of injurious insects to be controlled. Examples of injurious insects which can be controlled according to the method of the present invention are those belonging to the order of lepidopteron such as Spodoptera litura Fabricius, Egyptian cotton leafworm, pink bollworm, and Heliothis assulta GUENEE.
The amount (per unit area of a field) of a sex pheromone to be released from a source thereof distributed over a field is, in principle, selected depending on the area of the field, conditions of field products and vermination-conditions of individual injurious insects to be controlled. More specifically, a sex pheromone-release agent having an effective component-release rate ranging from 0.01 to 2 g/day is distributed in the central region of a field to be controlled at a density ranging from 1 to 50 locations/ha. On the other hand, a sex pheromone-release agent having an effective component-release rate ranging from 0.001 to 0.05 g/day is uniformly distributed around the peripheral region of the field at a density ranging from 500 to 2000 locations/ha. In other words, a sex pheromone-release agent having a high release rate per unit time is distributed over the central region of a field to be controlled at a low density, while a sex pheromone-release agent having a low effective component-release rate (per unit time) is distributed over the peripheral region of the field at a high density.
The distribution of the sex pheromone-release agent around the periphery of the field may be performed by stretching a rope in which the sex pheromone-release agent is enclosed. The effective component-release rate of the rope enclosing the sex pheromone-release agent preferably ranges from 5 to 250 mg/m/day. Such a sex pheromone-release rope is stretched around the periphery of a field at a density ranging from 10 to 150 m/ha.